1. Field of the Invention
The present invention relates to a resistance change type memory, and particularly to a memory in which a resistance change type storage element is used.
2. Description of the Related Art
Recently, attention is focused on a memory in which a resistance change type storage element is used. In the resistance change type storage element, data can electrically be rewritten.
A phase change memory can be cited as an example of such memory. In the phase change memory, a phase change between an amorphous state and a crystalline state is utilized in a material used for a memory element. In the phase change memory, the data is stored in a storage layer of the memory element, and a transition of a phase state of the storage layer is reversely made between the crystalline state (low-resistance state) and the amorphous state (high-resistance state) by a current passed through the storage layer. States of data are distinguished according to a high-resistance state and a low-resistance state of a storage layer, and the data is stored in a nonvolatile manner.
A Resistive Random Access Memory (ReRAM) can be cited as another example of the memory in which the resistance change type storage element is used. There are two well known operation types in the resistance change type storage element used for ReRAM.
One of the two operation types is referred to as bipolar type. In the bipolar type, the high-resistance state and the low-resistance state are switched by changing a polarity of an applied voltage.
The other operation type is referred to as a unipolar type. In the unipolar type, the high-resistance state and the low-resistance state are switched by controlling a voltage value (current value) and an applied time (pulse width) of the voltage (current).
In the memories in which the resistance change type storage element is used, various circuit configurations and operations have been studied in order to enhance the operational reliability or performance.
For example, in a technique disclosed in U.S. Pat. No. 7,443,712, a capacitive element is connected to a bit line, and the data stored in the resistance change type storage element is erased by utilizing Joule heat generated by a discharge current of the capacitive element.